Network systems provide a capability to transport data from various sources to various destinations. However, user demands for data transport capability tend to increase over time. Thus, it is necessary to provide an ability to expand the capability of network systems. Network systems are typically provided in housings of standardized dimensions, such as those that allow mounting in an equipment rack. Thus, efforts are typically made to provide as much data transport capability as possible using existing technology within the confines of the standardized dimensions. As an example, one housing of rack-mountable equipment may be referred to as a shelf. Within that shelf, a plurality of subsystems of a network system may be mounted. As the demand for data transport capability exceeds that provided by one shelf, it may be desirable to expand the network system from a single shelf network system to a multiple shelf network system. Different approaches to providing for such expansion have been tried with varying results.
FIG. 1 is a block diagram of an existing technique for expanding a single shelf network system by interconnecting two single shelf network systems using input/output cards. A first single shelf network system 101 includes switching fabric 104, control card 105, and input/output (I/O) cards 106–108. A second single shelf network system 102 includes switching fabric 109, control card 110, and I/O cards 111–113. I/O card 108 is coupled to I/O card 113 via link 103.
The technique of FIG. 1 suffers from several disadvantages. For example, the bandwidth of link 103 is necessarily limited by the bandwidth of I/O cards 108 and 113. Thus, unless at least half of the switching capacity in each shelf is dedicated to interconnection of the two single shelf network systems, non-blocking communication between the two single shelf network systems cannot be provided. Non-blocking communication is desirable in that it provides the ability of the full bandwidth of network traffic originating at each of several nodes of a network to be passed to among the several nodes in any combination without constraint, loss, or delay of the network traffic. The analogous example of non-blocking communication in traditional telephony is that an arbitrary half of all subscribers can call each call a unique subscriber among the remaining half of all subscribers in any combination without anyone receiving a busy signal. By not practically supporting non-blocking communications, the technique of FIG. 1 increases the likelihood of network congestion and loss or delay of data.
Another disadvantage of the technique of FIG. 1 is that both data and control information are carried over link 103. Thus, it is not possible to guarantee that control information will not adversely affect the transmission of the data. For example, control information might inadvertently be propagated to other network nodes, and those network nodes might incorrectly interpret the control information or be unable to interpret the control information, resulting in degradation of network performance or network failure. Also, in the event of a failure in either of the single shelf network systems, any attempt to isolate data between the two single shelf network systems will also cut off any communication of control information between the two single shelf network systems, thereby complicating or preventing effective diagnosis of the failure. Additionally, as more control information is passed between the two single shelf network systems, the amount of available bandwidth for communication of data is correspondingly reduced. Thus, shortages of data bandwidth may be experienced.
FIG. 2 is a block diagram of an existing technique for expanding a single shelf network system by interconnecting two single shelf network systems by installing expansion cards in dedicated expansion card slots. Single shelf network system 201 includes switching fabric 204, control card 205, I/O cards 206 and 207, and dedicated expansion card slot 208, which is not available for use with an I/O card. Single shelf network system 202 includes switching fabric 209, control card 210, I/O cards 211 and 212, and dedicated expansion card slot 213, which is not available for use with an I/O card. As can be seen, within the physical constraints of a given housing, the provision of space for dedicated expansion card slots necessarily reduces the space available for I/O cards, and, therefore, the number of I/O cards that can be supported. Consequently, the overall data bandwidth capability is correspondingly reduced. Additionally, the technique illustrated in FIG. 2 also suffers from disadvantages mentioned above in reference to FIG. 1. For example, the prevention of interference to data communication by control information cannot be guaranteed. Also, diagnosis of failures is complicated, as described above.
As can be seen, existing techniques for expansion of single shelf network systems exhibit numerous deficiencies. Thus, a technique is needed that provides for expansion of single shelf network systems without the disadvantages that result from existing techniques.